This invention concerns fine coagulated particles of ultrafine monoclinic zirconia crystals oriented in a fiber bundle-like form and a method of manufacturing them. More specifically, it relates to fine coagulated particles of ultrafine monoclinic zirconia crystals in which primary particles of ultrafine monoclinic zirconia crystals oriented to join into fibers of less than 50 .ANG. diameter in the direction of C-axis are gathered in the bundle-like form of 300 to 2000 .ang. width and 2000 to 10000 .ANG. length, as well as a method of manufacturing them.
Since fine anisotropic particles extended in one direction are easily oriented by the external force or flowing in the molding step, they are applied to various kinds of oriented ceramics. Anisotropic zirconia particles are considered essential for providing orientation in the texture of ceramics using zirconia starting material, partially stabilized zirconia or piezoelectric or ferroelectric materials.
The present inventor has already filed patent applications regarding anisotropic zirconia particles intended for such a purpose.
One of the patent applications concerns oriented coagulated particles of zirconia type crystals prepared by subjecting an aqueous solution of a zirconium salt or a liquid suspension mixture of the aqueous solution with zirconium hydroxide to a heat treatment under an acidic condition of lower than pH 7 to form fine monoclinic zirconia crystals, then subjecting the fine crystals to a heat treatment in an aqueous strong alkali solution such as of KOH under the presence of zirconium hydroxide at a temperature of higher than 90.degree. C. and then preferentially growing the zirconia crystals in a specific direction (refer to Japanese Patent Laid-Open No. 180917/1985).
Another of the patent applications concerns a method of preparing a sol of flaky crystalline zirconia by subjecting a water soluble zirconium salt or ultrafine crystalline zirconia obtained through hydrolysis of the salt under heating to a heat treatment in an aqueous solution containing hydrochloric acid or nitric acid at a high concentration of greater than 5N under the temperature from 120.degree. to 250.degree. C. for more than 50 hours (refer to Japanese Patent Laid-Open No. 201622/1986).
A further patent application concerns a method of preparing flaky zirconia type fine crystals as a layered structure of less than 500 .ANG. thickness containing metal ions mainly composed of Zr and sulfate ions (refer to U.S. patent application Ser. No. 881,812).
The foregoing patent applications disclose anisotropic particles respectively having features different from each other and the present inventor has continued a further study and accomplished this invention based on the finding for the method of manufacturing novel fine coagulated particles of monoclinic ultrafine zirconia crystals oriented in a fiber bundle-like form.